1. Field of the Invention
The present invention relates to an ink jet apparatus which discharges ink as ink droplets.
2. Discussion of the Background
Conventionally, an ink jet apparatus such as an ink jet printer discharges ink in an ink jet head from nozzles as ink droplets, onto a printing medium, thereby performs image formation.
In this ink jet apparatus, the ink is supplied from an ink tank or the like to the ink jet head via an ink channel. When the ink contains foreign materials, clogging occurs in the nozzles of the ink jet head, which causes ink discharge failure. Accordingly, a filter for removal of foreign materials is provided in the ink channel, whereby the entrance of foreign materials contained in the ink into the ink jet head can be prevented.
On the other hand, as an ink tank, a removable ink cartridge or the like is employed. Upon change of the ink cartridge, when the ink cartridge is removed from the ink jet apparatus, the ink channel is opened to the atmosphere and bubbles may enter the ink channel. In such state, when the ink is supplied from the ink cartridge to the ink jet head, the bubbles move together with the ink to the ink jet head side. The bubbles may be captured with the filter and stay on it or may pass through the filter and enter the ink jet head. Then ink supply may be unstable due to the bubbles stay on the filter, and further, ink discharge failure may occur due to the bubbles in the ink jet head. This may become a factor of poor printing to a printing medium.
To solve this problem, proposed is a method for preventing entrance of bubbles in an ink jet head by providing a buffer tank in an ink channel connecting an ink tank to the ink jet head (Japanese Published Unexamined Patent Application No. 2003-19811).
Further, proposed is a method for automatically removing bubbles captured with a filter in an ink channel by shaping the ink channel to spread toward the filter (Japanese Published Unexamined Patent Application No. 2001-171142).
Further, proposed is a method for removing bubbles staying in an ink channel by idle-discharging ink between two nozzle suction operations in the ink jet head (Japanese Published Unexamined Patent Application No. 2001-105629). That is, the bubbles attached to and staying in the ink channel are made movable by ink idle discharging, and the bubbles are removed by the suction operation.
However, according to Japanese Published Unexamined Patent Application Nos. 2003-19811 and 2001-171142, since the entrance of bubbles in the ink jet head is prevented with the filter, once bubbles enter the ink jet head, the bubbles cannot be removed without difficulty.
Further, the entrance of bubbles in the ink jet head does not occur only by entrance of bubbles in the ink channel upon change of ink cartridge. That is, bubbles may be generated from air sucked from the nozzles due to change of temperature or atmospheric pressure or from dissolved gas in the ink, and enter the ink jet head. Accordingly, such bubbles cannot be removed without difficulty by the above techniques disclosed in Japanese Published Unexamined Patent Application Nos. 2003-19811 and 2001-171142. With regard to the technique in Japanese Published Unexamined Patent Application No. 2001-105629, it is possible to remove bubbles in the ink jet head, however, as a suction mechanism or the like to implement the suction operation is required, the apparatus is increased in size. Further, the control for the apparatus is complicated, and the cost is increased.